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Fencer Intel
medium 6.5

CVE-2026-102821 json

Russh: Unbounded memory exhaustion via CHANNEL_OPEN flood during a client-stalled rekey

published last mo. modified last mo. also EUVD-2026-89204 , GHSA-35g8-35p8-c8fw

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 29%
public exploits
0
none known

Summary

Russh is a Rust SSH client and server library. Prior to 0.63.2, an authenticated remote peer can send SSH_MSG_KEXINIT without the required SSH_MSG_KEX_ECDH_INIT and then flood SSH_MSG_CHANNEL_OPEN messages while SessionKexState::InProgress prevents priority_receiver in russh/src/server/session.rs from being drained. The server continues processing network input and enqueues a ChannelOpenReply for each request on an unbounded channel, allowing one connection to grow memory until the process is terminated. This issue is fixed in version 0.63.2.

Patch / fix

  • crates.io russh 0.63.2
  • warpgate_project warpgate 0.63.2
  • russh_project russh 0.63.2
  • rust-russh Debian 14 0.64.1-1

debian advisories DEBIAN-CVE-2026-102821

  • openshell hummingbird 1 0.1.2-0.2.hum1
  • openshell-gateway hummingbird 1 0.1.2-0.2.hum1
  • python3-openshell hummingbird 1 0.1.2-0.2.hum1

red hat advisories RHSA-2026:74586

Is CVE-2026-102821 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-102821 updated cvss 6.5

russh: russh: Denial of Service via unbounded memory exhaustion during stalled key renegotiation

  • Red Hat Hardened Images openshell 0.1.2-0.2.hum1, openshell-gateway 0.1.2-0.2.hum1, python3-openshell 0.1.2-0.2.hum1
    fixed: vendor fix RHSA-2026:74586

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.36% chance of exploitation in the next 30 days, higher than 29% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/Eugeny/russh/security/advisories/GHSA-35g8-35p8-c8fw referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
crates.io russh
<0.63.2
0.63.2

Affected products

  • Eugeny russh

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.